Cycles Subsurface shader: GPU compute and CPU compute give totally different results
The SSS shader has not been implemented for GPU rendering yet. It will always render black.
Update: SSS now works on GPU, so they should look the same.

If you're looking for quick renders, SSS is not a good idea. If you can get away with a simple Diffuse BSDF shader with a bit of Translucent BSDF, that'd be great.